Thanks to a message from Lorrie Graham in Ancestry on the background of the McIntires I took another look at the mess. Nine years ago I wrote we had to bid goodbye to them because of a newspaper article saying that Elizabeth Smith was the sister of Capt. William Smith when she married Joseph Rippey. This, added to her DOB of 1798, meant that she could not be the daughter of William and Isabella McIntire.
But since 2007 Find-a-Grave has done great work. Their entry for the tombstone of Elizabeth McIntire Smith reads: 42 years, dau of William and Isabella McIntire. The "42 years" means she was born in 1777. That fits nicely with the new evidence on the marriage of the McIntires--August 4, 1774.
So the bottom line now is, assuming the accuracy of the Find-a-Grave data, we must assume either the newspaper article was in error in referring to "brother" rather than "father" William Smith, or that she had a brother William who hasn't shown up in other records. Either way we can return the McIntires to the ancestry of the Rippeys. More to follow.